It is as ridiculous as it sounds. There is simply no case at all where API use cannot be sensibly argued as fair use. That's why you use an API in the first place........

What privileges would such a copyright provide?

In practice? None.

> There is simply no case at all where API use cannot be sensibly argued as fair use.

An API being used by a client and an API being copied by a competitor to be used by those same clients are two completely different situations.

Nope, they aren't, or at the very least, the difference between them is as to be indistinguishable. That's what the jury decided here.

Using API and the word 'copied' in the same sentence simply doesn't mean anything.

I think you've just started to delve into the problem domain of copyright vs copyleft and why there are legal considerations when you allow people to access your software using an API.

Wave around a piece of legal paper with your name on it, if you file it with the copyright office.

And that's about it.